Ole Mars River

Meandering channels provide evidence for the Red Planet's watery past

Scientists still have not found the smoking gun that proves life ever existed on Mars. If it did, however, a new study points out a likely place

Courtesy NASA/JPL/Malin Space Science Systems

This meandering loop was part of a river system that once crossed the Martian plains.

where traces of it might be found: an ancient river system that snaked across the plains of Mars’s southern hemisphere some 3½ billion years ago. “This is the first really good evidence for persistent flow of a liquid in the Martian past,” says planetary geologist Ken Edgett of Malin Space Science Systems in San Diego.

High-resolution images collected by Mars Global Surveyor, which is currently orbiting the Red Planet, reveal a complex network of meandering channels, eight miles long by seven miles wide, located in what appears to be a river delta. The channels suggest that water once coursed across Mars and that these flows continued for quite some time—long enough to sculpt features resembling those of terrestrial river systems. For example, the images reveal a meandering loop, often seen in winding, slower moving streams. On Earth, such loops can eventually pinch off and evolve into independent, crescent-shaped bodies of water called oxbow lakes. Edgett and his colleagues have not found any equivalent formations on Mars, but they do see evidence of a secondary channel that diverted water from the main stream.

Water no longer flows through the channels, of course. In fact, they are no longer channels at all. After the Martian surface dried out billions of years ago, the barren channels were filled with sediment and, over time, buried completely. Eventually wind and sand erosion reversed the process, chewed away the overlying sediments, and exposed the cemented, coarse-grained floor of the ancient river system.

Edgett hopes this latest find will finally settle the long debate about whether Mars once had significant quantities of running water on its surface. “You can really quibble only about the details. It is undeniable that a liquid did this,” he says. “What are the choices for that liquid? Beer? Coca-Cola? We know that there is H2O in the polar caps and in the atmosphere, so you’d have to imagine some exotic, strange fluid on Mars if it weren’t water.” A full report on the Martian rivers appears in the November 13 issue of ScienceExpress, Science magazine’s fast-track online edition.